Editing Dalton (unit) (section)

=== Coulometry ===
{{main|Coulometry}}
The electric charge per [[mole (unit)|mole]] of [[elementary charge]]s is a constant called the [[Faraday constant]], ''F'', whose value had been essentially known since 1834 when [[Michael Faraday]] published [[Faraday's laws of electrolysis|his works on electrolysis]]. In 1910, [[Robert Millikan]] obtained the first measurement of the charge on an electron, −''e''.  The quotient ''F''/''e'' provided an estimate of the Avogadro constant.<ref name=ebrit1974/>

The classic experiment is that of Bower and Davis at [[NIST]],<ref>This account is based on the review in {{cite journal |author-first1=Peter J. |author-last1=Mohr |author-first2=Barry N. |author-last2=Taylor |title=CODATA recommended values of the fundamental physical constants: 1998 |journal=[[Journal of Physical and Chemical Reference Data]] |volume=28 |issue=6 |pages=1713–1852 |bibcode=1999JPCRD..28.1713M |doi=10.1063/1.556049 |year=1999 |url=https://www.nist.gov/pml/div684/fcdc/upload/rmp1998-2.pdf |archive-url=https://web.archive.org/web/20171001122752/https://www.nist.gov/sites/default/files/documents/pml/div684/fcdc/rmp1998-2.pdf|archive-date=2017-10-01}}</ref> and relies on dissolving [[silver]] metal away from the [[anode]] of an [[electrolysis]] cell, while passing a constant [[electric current]] ''I'' for a known time ''t''. If ''m'' is the mass of silver lost from the anode and ''A''{{sub|r}} the atomic weight of silver, then the Faraday constant is given by:
{{block indent|<math>F = \frac{A_{\rm r}M_{\rm u}It}{m}.</math>}}
The NIST scientists devised a method to compensate for silver lost from the anode by mechanical causes, and conducted an [[isotope analysis]] of the silver used to determine its atomic weight. Their value for the conventional Faraday constant was ''F''{{sub|90}}&nbsp;= {{val|96485.39|(13)|u=C|up=mol}}, which corresponds to a value for the Avogadro constant of {{val|6.0221449|(78)|e=23|u=mol-1}}: both values have a relative standard uncertainty of {{val|1.3|e=-6}}.